腸道沙門氏菌為食物病原菌之一，其中Salmonella typhimurium LT2菌株之基因序列因已全數解碼，且與模式細菌大腸桿菌之基因組具高相似性，而成為主要研究用微生物之一。甲硫胺酸的合成為細菌生長所必需之重要代謝途徑，其合成路徑之最後一步的作用酵素MetE (甲硫胺酸合成酶) 為合成過程中必須酵素之一。本研究藉由建立沙門氏菌染色體之基因庫，在全基因體層級中篩選出可調控沙門氏菌metE表現之影響因子。研究結果發現metE基因表現會受metB、rseB、ycjE、fabI、nifU和nifS等基因產物影響。由篩選所得基因功能分布之廣泛，推測腸道沙門氏菌metE以及甲硫胺酸的生合成在細菌體內應受到複雜的調控。而本研究使用之建構基因庫篩選影響因子的方法亦可應用於其他基因調控之研究。

Enteric Salmonella is one of the food microbial pathogens. Among all the subspecies, Salmonella typhimurium LT2, of which chromosomal DNA has been sequenced and found out to be similar to that of Escherichia coli, is one of the major microorganisms for the current research study. Methionine biosynthesis is an essential metabolic pathway for bacterial growth. The final step for methionine biosynthesis is mediated by the metE-encoded MetE enzyme (cobalamin-independent methionine synthase). In this study, via constructing the Salmonella chromosomal DNA library, we identified the regulators of metE through a genome-wide screen. Our results revealed that the genes rseB, metB, ycjE, fabI, nifU, and nifS may encode the products that affect the expression of metE. These genes fall into catagories with a wide variety of cellular functions, suggesting the expression of metE as well as methionine biosynthesis may be under complicated regulations in enteric Salmonella. Furthermore, the gene-library based screening method used in this study is also likely to be applied for other related study.